Fire Alarm Systems

In simple terms a fire alarm system is a number of automatic or manual devices linked and designed to alert the presence of fire.

The British Standards BS5839 Part 1 splits fire alarm systems into 3 different categories.

Category M Systems – This can be manual only ie.. hand bells, gongs etc.. where the operate would be required to discover the fire and then take action to alert others and / or the fire brigade. Or it could be a manual electric system that would rely on break glass call points at the route of exit and sounders to alert other building occupants. These systems would only be used for places where risk is low in terms of occupancy number and there is not sleeping risk.

Category P System – The main aim of a Cat P System is the protection of property

Cat P systems are further subdivided into 2 categories, P1 where the main objective is to provide the earliest possible warning of a fire. The purpose is to minimise the time between ignition of fire to the arrival of your local a fire brigade. By reducing this time period it will off course reduce the risk of potential damage to the property. The other category of P systems is P2 and the main difference in this is where a P1 is designed to protect the whole building a P2 system is based around specific areas of the building that are seen as being a risk of fire or hazard.

Category L Systems – The main aim of a Cat L System is the protection of life.

Again a CAT L System is further subdivided but this time into 5 sub categories.

L1 – BS5839 classification L1 must include automatic fire detection in all rooms, all escape routes and any void area over 800mm in height. Sounders must also be present throughout the building and achieve a minimum sound level of 65dB(A) throughout and 75dB(A) at any bedhead where there use presents is a sleeping risk. In areas of high ambient noise sound levels should be 5dB(A) above the normal noise level of that area although not exceeding 120dB(A).

L2 – BS5839 classification L2 again should include automatic fire detection on all escape routes and any room leading onto escape routes. An L2 system may also include additional areas that are not included as escape routes such as boiler / plant rooms, kitchens etc. Sounders must also be accordance to BS5839 Category L1 description as above.

L3 – BS5839 classification L3 system is similar to an L2 system in the sense that it must have automatic fire detection positioned on escape routes and adjoining rooms, but it does include for additional areas deemed to be high fire risk. The sounders again will be according to the description in the BS5839 Category L1 description as above.

L4 – BS5839 Classification L4 system includes automatic fire detection on escape routes only, sounders in an L4 system must again be in accordance to the description in the BS5839 Category L1 description as above.

L5 – BS5839 Classification L5 System is designed for buildings that have a particular fire risk. It could be classed as an “custom design” or “an all other situations” where the size or usage of the building may suggest that it a manual system is required, however there has been certain areas identified that are deemed as high risk and therefore some automatic detection is required. Examples of this might be a small office that has a garage or storage area off it that contains paint or gas bottles. An open planned office with limited staff but they might have a server room with high value or high risk items in terms of fire. Sounders for an L5 system should still be in line with the description in the BS5839 Category L1 as above.

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